Sensitizer for photothermographic substances



United States Patent SENSITIZER FOR. PHOTOTHERMO GRAPHIC.

' SUBSTANCES I Marilyn Levy, Red Bank, N. J., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Application July 28, 1954, Serial No. 446,428

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

The invention relates to modifiers for photothermographic substances and for layers sensitized with such modified photothermographic substances. These modifiers may not be in themselves photothermographic but have the property of modifying the sensitivity of at least some of the known photothermographic substances.

The term photothermographic has been defined in U. S. Patent 2,059,839 as characterizing a material which after its exposure to light may be decomposed by the action of heat differentially in accordance with the exposure to light. A photographic layer sensitized with such photothermographic substances is therefore, after exposure to light, developable by heat.

The present invention is based on the discovery that the light sensitivity of most known photothermographic silver salts may be modified by the addition of Wetting agents or surface-active agents. These modifiers may either increase or decrease the light sensitivity of the photothermographic silver salt.

The invention will become more apparent from the following description of embodiments of the broad inventive idea.

Example 1 Wet 0.75 gram of silver succindiamidoxime with ml. of gelatin (3% at 40 C.) with agitation. Add ml. of gelatin (3%) followed by 5 ml. of a 2% solution of a wetting agent, e. g., sodium lauryl sulfate. Pass through a stainless steel homogenizer (warmed) and coat on clean glass slides. The slides may then be exposed to light and thermally developed at about 104 C. The light sensitivity of such layers increases with increased percentages of the wetting agent added.

The light sensitivity of a water solution of silver succindiamidoxime is also increased by the addition of sodium lauryl sulfate.

Example 2 Example 3 Wet 0.70 gram silver oxalate with 5 ml. of a 3% gelatin solution at 40 C. Add remaining 10 ml. of gelatin with agitation. When the silver salt is well dispersed,

2,756,l46 Patented July 24, 1956 add S-ml. of a 2% solution of a wetting agent such as sodium lauryl sulfate, sodium Z-ethylhexene sulfonate, or sodium tetradecyl sulfate. Pass through a stainless steel homogenizer (warmed) and coat on glass slides. The slides may then be exposed to light and thermally developed.

The light sensitivity of the above-described emulsion using silver oxalate is considerably increased by the above-mentioned wetting agents. A similar effect is obtainable by using silver citrate or silver acetate as the photothermographic substance. Polyethylene glycol alkyl ethers have only a slight effect on the light sensitivity of these silver salts.

The ratio of the wetting agent to the photothermographic silver salts used in the preparation of photothern'iographic emulsions in gelatin may vary within considerable limits. Too large a percentage of a Wetting agent usually gives a discontinuous film on glass with gelatin as the vehicle. Generally, satisfactory results are obtained with layers prepared from emulsions containing about 2.1% gelatin, 0.5 to 1.0% wetting agent, 3.6% silver salt and between 93.8 and 93.3% water.

The light sensitivity of some of the known photothermographic substances may be decreased by some of the modifiers mentioned above. It was found, for instance, that the light sensitivity of silver thiosemicarbazide is increased by the addition of sodium 2-ethylhexene sulfonate, but decreased by the addition of sodium heptadecyl sulfate, sodium dioctyl phosphate, sodium tetradecyl sulfate, polyethylene glycol alkyl ethers, and sodium lauryl sulfate.

The photothermographic substances modified according to the invention may be dispersed in any suitable colloid carrier to produce a modified photothermographic layer on one of the conventional supports. The material for the photothermographic layer may conventionally consist of gelatin, caesin, agar, or various natural or synthetic high polymers such as polystyrene or phenol formaldehyde resins, vinyl resins, alkyd resins, etc. The support for the modified photothermographic layer may be a plate of any of the commonly used material such as glass, paper, cellulose derivatives, etc.

The invention is not limited to the specific modifiers described above but can also be used in connection with other surface active or wetting agents which have the capacity of modifying (increasing or decreasing) the light sensitivity of photothermographic substances.

It will be obvious to those skilled in the art that many variations and combinations of photothermographic silver salts and wetting agents are possible within the broad inventive idea as characterized in the appended claims.

What is claimed is:

l. A photothermographic element comprising a colloid carrier having dispersed therein a member of the group of photothermographic silver salts consisting of silver succindiamidoxime, silver oxalate, silver citrate, silver acetate and a member of the group of Wetting agents consisting of sodium lauryl sulphate sodium Z-ethylhexene sulfonate, sodium Z-ethylhexene sulfonate, sodium tetradecyl sulfate, sodium dioctyl phosphate, sodium heptadecyl sulfate, polyethylene glycol alkyl ethers.

2. A photothermographic element according to claim 1 comprising about 2.1% gelatin, 0.5 to 1.0% of said wetting agent, 3.6% of said photothermographic silver salt and 93.8% to 93.3% water.

3. A photothermographic element according to claim 1 in which the photothermographic silver salt consists of silver succindiamidoxime.

4. A photothermographic element according to claim 1 in which the photothermographic silver salt consists of silver oxalate.

5. A photothermographic element according to claim References Cited in the file of this patent 1 in which the photothermographic silver salt consists of UNITED STATES PATENTS silver citrate.

6. A photothermographic element according to claim 1 3 1 2315121; et a1. gif -2g, h th i1 t 5 e- In W 1611 the Photo m graphlc s ver salt 0011815 5 of 2,304,900 Stasiw Dec 15 1942 Silver acetate- 2,368,287 Chilton Ja 30 1945 

1. A PHOTOTHERMOGRAPHIC ELEMENT COMPRISING A COLLOID CARRIER HAVING DISPERSED THEREIN A MEMBER OF THE GROUP OF PHOTOTHERMOGRAPHIC SILVER SALTS CONSISTING OF SILVER SUCCINDIAMIDOXZIME, SILVER OXALATE SILVER CONSISTING OF SILVER ACETATE AND A MEMBER OF THE GROUP OF WETTING AGENTS CONACETATE AND A MEMBER OF THE GROUP OF WETTING AGENTS CONSISTING OF SODIUM LAURYL SULPHATE SODIUM 2-ETHYLHEXENE SULFONATE, SODIUM 2-ETHYLHEXENE SULFONATE, SODIUM TETRADECYL SULFATE, SODIUM DIOCTYL PHOSPHATE, SODIUM HEPTADECYL SULFATE, POLYETHYLENE GLYCOL ALKYL ETHERS. 